Project Abstract. 13C NMR is a powerful tool for following the metabolism of strategically labeled 13C substrates in isolated cells, perfused organs, animals and humans. Analysis of relative fluxes through competing or bifurcating pathways using 13C isotopomer analyses has been the focus of this NIH funded project for the past 19 years. Although powerful, 13C isotopomer methods mostly require metabolic steady- state conditions and sufficient sample to allow collection of 13C NMR spectra over reasonable scan times. With recent advances in dynamic nuclear polarization (DNP) device technology, one can now reliably achieve sensitivity enhancements of 5,000-fold and often as much as 10,000-fold for detection of 13C metabolites in tissues. Such sensitivity gains offer the exciting possibility of applying the metabolic tools developed over the years with support from this grant to achieve real-time 13C imaging of metabolism in vivo. Initial hyperpolarized 13C results obtained in our laboratory using a newly acquired DNP device have shown that it is now possible to measure flux through pyruvate dehydrogenase (PDH) in isolated, perfused rat hearts using hyperpolarized [1-13C]pyruvate. Given that flux through PDH is known to be modified in ischemic heart tissue and in other diseases including diabetes and cancer, the use of hyperpolarized 13C substrates to measure absolute flux through important pathways such as this in vivo would not only revolutionize clinical diagnostic imaging but also serve as an important tool to better understand the metabolic effects of new drugs aimed to combat these diseases. The goal of the proposed new work is to develop hyperpolarized 13C methods to measure flux through several specific enzyme catalyzed steps in perfused hearts, livers and neoplastic tissues. Approaches are described to measure flux through the oxidative branch of the pentose phosphate pathway (PPox) and TCA cycle flux (VTCA) in perfused hearts, livers and cancer cells under various altered physiological conditions and gluconeogenic flux in perfused mouse livers. Hyperpolarized 13C substrates return to normal Boltzman polarization levels with a time constant of T1 so an emphasis is placed on the proper design of long T1 carbons in substrates that participate in these reactions. Proper analysis of time-dependent hyperpolarized 13C NMR data will require development of mathematical models to fit kinetic curves for appearance and disappearance of the hyperpolarized substrates and their enzyme-catalyzed products. In all cases, flux values measured by hyperpolarized 13C NMR will be compared with gold standard measures of flux through these same reactions. Once these methods are established, the long-term goal of this project is to image these biological processes in real-time and in multiple organs in vivo. Two high priority targets are to image glucose production (gluconeogenesis) in diabetic animal models in vivo and to establish methods to image tissue redox in vivo. Project Narrative: 13C NMR is a powerful tool for following the metabolism of 13C-enriched substrates in isolated cells, perfused organs, animals and humans. Conversion of one metabolic intermediate in units of moles/min is referred to as flux through a pathway. The development of 13C isotopomer analyses, the focus of this NIH funded project for the past 19 years, allows a measure of relative flux through pathways but not absolute flux. It is important to develop new methods to measure absolute flux in vivo because altered flux through pathways is the basis of many common disease states. Recent advances in dynamic nuclear polarization (DNP) technology offers the possibility of detecting 13C metabolites with sensitivity enhancements of as much as 10,000-fold. Such sensitivity gains offer the exciting possibility of applying the metabolic tools developed over the years with support from this grant to achieve real-time 13C imaging of metabolism in vivo. Initial hyperpolarized 13C results obtained in our laboratory using a newly acquired DNP device have shown that it is now possible to measure flux through pyruvate dehydrogenase (PDH) in isolated, perfused rat hearts using hyperpolarized [1-13C]pyruvate. Given that flux through PDH is known to be modified in ischemic heart tissue and in other diseases including diabetes and cancer, the use of hyperpolarized 13C substrates to measure absolute flux through important pathways such as this in vivo would not only revolutionize clinical diagnostic imaging but also serve as an important tool to better understand the metabolic effects of new drugs aimed to combat these diseases. The goal of the proposed new work is to develop hyperpolarized 13C methods to measure flux through several specific enzyme catalyzed steps in perfused hearts, livers and neoplastic tissues. Two high priority targets are to image glucose production (gluconeogenesis) in diabetic animal models in vivo and to establish methods to image tissue redox in vivo.